Aggression

• The limbic system is a series of areas in the brain that help us to regulate our emotions. It involves the hypothalamus, hippocampus, amygdala and the thalamus.
• The amygdala is involved in evaluating the emotional importance of sensory information and providing an appropriate response. The more responsive the amygdala, the more likely a person will show aggressive behaviour.
• The hippocampus is involved in the formation of long-term memory which allows you to compare your past experiences of threat with the current situation to help people decide the appropriate behaviour to show.
• Gospic et al. (2011) provided support for this idea using the ultimatum game. Participants were asked to take the money someone had split with them or leave it. Sometimes participants were given unfair splits. They found when participants rejected unfair offers, their amygdalas were highly active.
• Gospic et al. also found when participants were given a benzodiazepine drug (which reduces the arousal of the limbic system) before the task, it halved the number of rejections and decreased the activity of the amygdala. This shows that the limbic system may be involved in aggressive behaviour.
• Serotonin is a neurotransmitter, which is involved in passing messages across the brain. One of its roles is to inhibit neural activity.

  Normal levels of serotonin in the orbitofrontal cortex are linked with reduced firing of the neurones and increased self-control.

  Decreased levels of serotonin have an influence on this cortex and lead to reduced levels of self-control and increased levels of impulsive behaviour.
• The male sex hormone testosterone is involved in the development of masculine features such as facial and body hair. It also has a role in regulating social behaviour, which has been supported in several animal studies of several different species to have an impact on levels of aggression. Some evidence of this has been found in the human population, which found a positive correlation between testosterone levels of criminals and their aggressive behaviour.
• Neural means that it occurs between the synapses and are fast acting. The limbic system and serotonin are both neural explanations for aggression.
• Hormonal means it is carried through the bloodstream and are slower to act. Testosterone is a hormonal explanation for aggression.
• Strength of neural and hormonal explanations of aggression:

  • Drugs which increase levels of serotonin also decrease levels of aggression
  • There is research from monkeys who were fed on tryptophan which increases the levels of serotonin.
• Weaknesses of the neural and hormonal explanations of aggression:

  • The orbitofrontal cortex is separate from the limbic system but also pays a role in aggression
  • Mainly correlations but not necessarily causes of aggressive behaviour
  • The dual-hormone hypothesis suggests testosterone only has an impact when cortisol levels are high
• Genetic factors are genes consistent in DNA strands which decide your physical traits as well as neurotransmitter levels and the size of your brain. They therefore influence your psychological features.
• Twin studies have suggested that aggression might be inherited. Genes count for 50% variance in aggressive behaviour.
• Coccaro et al. found a 50% concordance rate for identical (monozygotic) twins and 19% in non-identical (dizygotic) twins in physical aggression. In verbal aggression it was 28% and 7% respectively.
• Adoption studies are used in order to separate out the genetic factors from the environmental factors.
• Rhee and Waldman carried out a meta-analysis of adoption studies of direct aggression and antisocial behaviour. They found that genetic influences account for 41% of the variance in aggression.
• Monoamine oxidase A (MAOA) is an enzyme which absorbs any neurotransmitters in the synaptic gaps which are not absorbed by the post-synaptic neuron. In particular, it absorbs any leftover serotonin.
• A dysfunction in this area can lead to abnormal activity of the MAOA enzyme and therefore affects a person’s behaviour.
• A variant of the MAOA gene leads to low MAOA activity in the brain and has been associated with high levels of aggression.
• Research has found that those with the variant (MAOA-L) show higher levels of aggressive behaviour (Caspi et al.). This is because serotonin is left in the synapse rather than being reuptaken, which can lead to impulsive behaviour.
• As genes do not function in isolation, it is likely that the influence of the MAOA gene can only be linked to aggression when combined with early traumatic life events.
• Frazzetto et al. found a link between higher levels of aggression and low-activity of the MAOA gene but only in cases where participants had experienced severe trauma such as a sexual assault or physical abuse, during the first 15 years of their lives.

  This provides support for the diathesis-stress model.
• Strengths of genetic factors in aggression:

  • Initial research into the effects of the MAOA gene of aggression was conducted on animals. This gave the opportunity to study the long-term implications of the MAOA gene on aggression
• Weaknesses of genetic factors in aggression:

  • There are multiple ways of measuring aggression, making it difficult to draw valid conclusions from the data about the role of genetics in aggression.
  • It is likely that more than one gene can cause aggressive behaviour. This is important as it shows that the theory may be reductionist.
  • A problem with adoption studies is that they are difficult to show cause and effect, which makes it challenging to draw valid conclusions.
• Ethology is the study of animal behaviour in natural settings. It is not applied to humans. Lorenz is the founder of ethology.
• Ethologists suggest aggression can be studied in animals and be applied to humans because we are all subject to the same forces of natural selection.
• Evolutionary adaptive functions of aggression

  Animals do the same species don’t tend to kill each other in fights as they do not want to reduced the number of their species. However, when one of them loses they leave the area and spread out over a wider area, so they dominate more of the land. This is beneficial to survival as aggression helps to establish a hierarchy. This happens in humans too as Pettit et al. found children showed aggressive behaviour towards peers and then had power over others.
• Ritualistic aggression:


  Often animals do not fight each other, but instead show displays of aggression. These are helpful to show others their strength, so that it doesn’t escalate to a fight which can be physically costly and dangerous. These threats may make others back down from a fight.
• Anthropologists have found that humans also show ritualised aggression. Gardner and Heider found that the Dani of New Guinea often showed ritualised aggression through banging their spears on the ground and the calling tones they made towards other groups.
• Innate releasing mechanisms are hard-wired brain networks that respond to specific stimuli (signs or releasers) by initiating a fixed action pattern, a set or sequence of behaviours.
• A fixed action pattern is an adaptive sequence/stereotyped/ritual behaviours.
• Fixed action patterns have 6 main features:

  • stereotyped or relatively unchanging sequences of behaviour
  • universal - found in all species
  • unaffected by learning
  • ballistic - once the behaviour is triggered it always follows the same sequence
  • single purpose - only in a specific situation
  • a response to a specific sign
• Strengths of the ethological explanation of aggression:

  • there is evidence to support innate releasing mechanisms and fixed action patterns. Tinbergen found male stickleback fish were more aggressive in mating season, when they develop a red spot.
• Weaknesses of the ethological explanation of aggression:

  • there are cultural differences in levels of aggression. Nisbett found white males in southern states were more likely to become aggressive than those in northern states.
  • the view that aggression has evolved into a self-limiting and relatively harmless ritual has been challenged by observational research.
  • huge generalisations are made to humans. For example, Lorenz didn’t study higher order thinking animals such as primates.
• Evolutionary explanation for aggression is an evolutionary reason for men and does not try to explain women.
• Aggression is a strategy that would have been effective for solving several adaptive problems among early humans, for example: women cheating on their partner. Solving these problems enhanced the survival and reproductive success of the individual.
• Sexual jealousy is a major motivator of aggressive behaviour in males. This is because males could never be sure that they truly had fathered the child which they were supposed to be looking after and protecting. This is called cuckoldry.
• Strategies to reduce sexual infidelity are also called mate-retention strategies.
• Violence towards partner or potential love rival is a strategy to reduce sexual infidelity that was proposed by Buss. It is physically showing aggression towards their partner or someone they believe to be giving affection towards/ getting affection from.
• Direct guarding is a strategy to reduce sexual infidelity that was proposed by Wilson and Daly. It involves male vigilance over a partners behaviours. For example, checking who they are seeing or keeping tabs on them.